1. Field of the Invention
The present invention relates to optical lenses for glasses, contact lenses and intraocular lenses (IOLs), more particularly, to an improved ophthalmic lens (for prescription and non-prescription glasses, sunglasses, contact lenses and intraocular lenses or “IOLs”) incorporating dual filters that combine to provide protection against macular degeneration by reducing harmful light transmission and ocular photochemical damage.
2. Description of the Background
The goal of most protective lenses (including those in high-end sunglasses) is to provide a particular light transmission profile that yields the highest protection and perfect vision under all light conditions. To accomplish this goal, lenses for protective eyewear and IOLs often include filters that achieve a particular transmission profile. There are different perspectives on the optimum transmission profile what the best transmission profile is.
The ocular hazards from ultraviolet solar radiation are well established. Ultraviolet radiation falls within a range of wavelengths below visible light, generally between 100 and 400 nanometers. Long UVA radiation occurs at wavelengths between 315 and 400 nanometers. UVB radiation occurs between 280 and 315 nanometers. UVC radiation occurs between 200 and 280 nanometers. Wavelengths between 100 and 200 nanometers are known as vacuum UV. Vacuum UV and UVC are the most harmful to humans, but the earth's ozone layer tends to block these types of ultraviolet radiation. According to Prevent Blindness America, the American Academy of Opthalmology, and the American Optometric Association, the hazards from ultraviolet exposure include eyelid cancer, cataract, pterygium, keratitis, and macular degeneration. Cataracts are a major cause of visual impairment and blindness worldwide. “We've found there is no safe dose of UV-B exposure when it comes to the risk of cataracts, which means people of all ages, races and both sexes, should protect their eyes from sunlight year-round.” Infeld, Karen, Sunlight Poses Universal Cataract Risk, Johns Hopkins Study http://www.eurekalert.org/releases/jhu-sunposcat.html (1998). Indeed, age-related macular degeneration (AMD) is the leading cause of blind registration in the western world, and its prevalence is likely to rise as a consequence of increasing longevity. Beatty et al., The Role of Oxidative Stress in the Pathogenesis of Age-Related Macular Degeneration, Survey of Opthalmology, volume 45, no. 2 (September-October 2000).
More recently, the Age-Related Eye Disease Study (AREDS) was published. This was a major clinical trial sponsored by the National Eye Institute, one of the Federal government's National Institutes of Health. The AREDS investigated the history and risk factors of age-related AMD, as well as how to reduce the risk of advanced age-related AMD and its associated vision loss. It was found that high levels of antioxidants and zinc significantly reduce the risk of advanced age-related AMD (reported in the October 2001 issue of Archives of Opthalmology).
What is less well-known is that visible blue light can contribute to age-related AMD and its associated vision loss, causing significant damage over time. The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. A typical human eye will respond to wavelengths from 400 to 700 nm. This visible blue light falling within the 400-475 nm range can also cause damage over time. A ten-year Beaver Dam Eye Study was completed and reviewed in the Arch Opthalmology, vol. 122, p. 754-757 (May 2004). This study proves a direct correlation between the incidence of blue light and AMD but does not attribute the correlation to any particular blue light wavelengths. A number of other references suggest a correlation between the visible blue light contribution of sunlight and AMD. See, for example, West S. K. et al., Arch. Ophthaomol., 1989; 107: 875; Cruickshanks K J et al., Arch. Ophthaomol., 1993; 111: 514; Young R. W., Survey Ophthaomol., 1988; 32: 252; Mitchell P. Et al., Survey Ophthaomol., 1997; 104: 770.
The present inventor contends that there is a significant need for protective lenses that selectively block visible blue light in the 415-475 nm range. As the entire population is potentially exposed to sunlight, the odds ratio of 13.6 and 2.19 for high exposure to visible blue light and AMD represent quite robust evidence in support of the sunlight/AMD hypothesis. Consequently, a lens that dramatically reduces visible blue light (preferably in combination with a high degree of UVA and UVB protection, and without sacrificing visual acuity) will preserve visual function, and would be advantageous to the user
This transmission profile is difficult to achieve with conventional lens technology. The Food and Drug Administration recommends that sunglasses, prescription or non-prescription, block 99% of UVB and 95% of UVA, and most sunglasses on the market meet these criteria. The American National Standards Institute (ANSI) rates nonprescription eyewear for their potential to protect the human eye against solar radiation. However, many feel that the ANSI Z80.3 standard falls short. For example, the Z80.3 standard does not require specific quantification of the precise transmittance of ultraviolet radiation, nor blue light or infrared radiation, or reflected or scattered solar radiation that is not transmitted through the lens but still reaches the human eye. Some sunglasses for outdoor enthusiasts can achieve 99% of both UVA & B reduction, but afford no protection against visible blue light. This is because the existing lens technologies only afford control over glare, as well as the UVA & UVB transmission profile of lenses. These technologies include polarizers, color filters and mirror coatings.
Polarizers eliminate the horizontal transmission of reflected light through the lens to the eyes of the wearer. The polarizing layer blocks light at certain angles, while allowing light to transmit through select angles. This helps to negate annoying glare reflected off other surfaces such as water, snow, automobile windshields, etc. A polarized filter is produced by stretching a thin sheet of polyvinyl alcohol to align the molecular components in parallel rows. The material is passed through an iodine solution, and the iodine molecules likewise align themselves along the rows of polyvinyl alcohol. The sheet of polyvinyl is then applied to the lens with colored rows of iodine oriented vertically in order to eliminate horizontally reflected light. The sheet of polyvinyl may be applied to a lens in one of two ways: the lamination method or the cast-in mold method. To polarize a glass lens, the lamination method is used whereby the polyvinyl filter is sandwiched between two layers of glass. For plastic lenses, the cast-in mold method is used whereby the polyvinyl filter is placed within the lens mold. Relevant prior art patents might be seen in the Schwartz U.S. Pat. No. 3,838,913 and Archambault U.S. Pat. No. 2,813,459. A significant benefit of polarized lenses is the elimination of glare from reflective surfaces such as water.
Color filters can also provide excellent ultraviolet obstruction properties. For example, U.S. Pat. No. 4,878,748 to Johansen et al. (SunTiger) issued Nov. 7, 1989 discloses an optical lens with an amber filter having selective transmissivity functions. This is the original “Blu-blocker” patent for amber lenses that includes a sharp cut-on filter that blocks harmful Ultraviolet radiation and blue light. A combination dye is used to substantially block all wavelengths between 300 and 549 nanometers. The lens is substantially transparent to wavelengths greater than 636 nm which are most useful for high visual acuity in a bright sunlit environment. Similarly, U.S. Pat. No. 5,400,175 (SunTiger) discloses an amber filter having a cut-on at 550 nm. However, color-differentiation is highly distorted due to the deep orange tint as their deep yellow-orange tint weakens color differentiation. Indeed, many tinted sunglasses do not provide the capability to recognize traffic lights or other necessary color cues.
Various mirror coatings have been available to the sunglass industry for decades. These mirror coatings can be applied to the front and/or back surface of a lens to further reduce glare and provide protection against infrared rays. Metallic mirrors comprise a layer of metal deposited directly on a glass lens to create the equivalent of a one-way mirror. See, e.g., U.S. Pat. No. 4,070,097 to Gelber, Robert M (1978). However, like polarizers, metallic oxide coatings are not color-selective and cannot selectively block visible blue light in the 400-475 nm range.
Rugate filters are a less well-known lens technology in the context of protective eyewear. A Rugate filter is an interference coating in which the refractive index varies continuously in the direction perpendicular to the film plane. The addition of a rugate filter to a lens can potentially block visible blue and UV light, while allowing other visible light to pass unimpeded. Rugate filters are wavelength specific filters that have existed for about a decade. Their simple periodic continuous structures offer a much wider set of spectral responses than discrete structures, and they typically exhibit a spectrum with high reflectivity bands. This allows the possibility of making high reflectivity mirrors with very narrow bandwidth. Moreover, they can be formed so as not to distort bandwidths outside the stop-bands. In contrast to tinted lenses, this provides the capability to recognize traffic lights and other necessary color cues. An overview of Rugate filter technology can be found at Johnson et al., “Introduction to Rugate Filter Technology” SPIE Vol. 2046, p. 88-108 (November 1993), inclusive of how a simple rugate filter is derived from Fourier analysis. Other examples can be found in U.S. Pat. No. 5,258,872 “Optical Filter” by W. E. Johnson, et al. and disclosed in U.S. Pat. No. 5,475,531 “Broadband Rugate Filter” by T. D. Rahminow, et al.
Despite the foregoing options, there currently are no protective lenses that can block visible blue light in the 415-475 nm range without otherwise degrading the visible light transmission spectra. The foregoing is possible by combining two filters to establish a selective light transmission profile under all light conditions that maximizes the degree of protection as well as clarity of vision. The present dual-filter ophthalmic lens technology can be incorporated in ophthalmic lenses, sunglasses, polarized sunglasses, intraocular lenses and contact lenses.